All-electrical valley filtering in graphene systems (II): Numerical study of electron transport in valley valves

TL;DR

This study numerically investigates electron transport in graphene-based valley valves, demonstrating on-off transmission contrast, robustness against impurities, and effects of strain, advancing the understanding of valleytronics device performance.

Contribution

It provides a detailed numerical analysis of valley filter-based graphene valves, highlighting effects of various scattering mechanisms and strain on electron transport.

Findings

Pronounced on-off contrast in electron transmission between valve configurations.

Enhanced contrast with increasing number of valley filters.

Robustness of valve performance against impurity and edge roughness scattering.

Abstract

This work performs a numerical study of electron transport through the fundamental logic gate in valleytronics - a valley valve consisting of two or increasing number of valley filters. Various typical effects on the transport are investigated, such as those due to interface scattering, long- and short- range impurity scattering, edge roughness, strain, inter-filter spacing, or increasing number of valley filters. For illustration, we consider the class of specific valves built from graphene quantum wire valley filters in single layer or bilayer graphene, with the filters subject to separate control of in-plane, transverse electric fields. The nearest-neighbor tight-binding model of graphene is used to formulate the corresponding transport problem, and the algorithm of recursive Green's function method is applied to solve for the corresponding transmission coefficient. In the case of two-filter valves, the result explicitly demonstrates the existence of a pronounced on-off contrast in electron transmission between the two configurations of valves, namely, one with identical and the other with opposite valley polarities in the two constituent filters. The contrast is shown to be enhanced when increasing the number of filters in valves. Signatures of Fano-Fabry-Perot type resonances in association with interface scattering and inter-filter spacing are illustrated. Electron backscattering due to impurities is found to be sizably suppressed, with the valve performance showing considerable robustness against edge roughness scattering. On the other hand, the presence of a uniaxial strain modifies the electron transmission and results in an interesting quasi-periodic modulation of transmission as we vary the strain strength.